This last Summer I visited Lowell Observatory in Flagstaff Arizona. I saw the telescope where Percival Lowell (1855-1916) convinced himself he saw canals on Mars. In science one can easily fall in love with a hypothesis and begin to see what you expect to see. After the Martian canals had been vanquished, and Perceval Lowell had passed away, a young Astronomer by the name of Clyde Tombaugh (1906-1997) took up his search for a ninth planet. Tombaugh painstakingly photographed the night sky and miraculously discovered a new planet (expected to be at least Earth-sized) in the expected area of the sky predicted in February of 1930. The amazing part, is how lucky Tombaugh had been. Pluto has a 17 degree tilt upward from the ecliptic, which means its not in the plane of the other planets—where one would expect to find it. Pluto was in a location where it was very close to the ecliptic—a rare occurrence. With an orbital period of 280 years, if Pluto had been in its farthest part of its orbit, Tombaugh would have gazed into empty space. In many ways he won a cosmic lottery ticket. The new planet became known as Pluto and as PL is also the initials of Percival Lowell, it was greeted with open arms at Lowell Observatory. All was fine until a team, lead by Mike Brown (1965- ) at Cal Tech, located Eris which is much farther out from the Sun than Pluto, and appeared to be larger than Pluto, was, for a while, considered Planet 10, with Pluto still designated as Planet 9.
Better measurements slowly reduced the mass, size and mathematical need for Pluto to provide an explanation of the now nonexistent gravitational perturbations. As we all know now, Pluto is at best considered a dwarf planet in the Kuiper Belt. After Pluto’s change in categorization, it stopped being the last planet discovered, and became the first Kuiper Belt object discovered. Planet 9 then vanished in an organizational puff of smoke. The description of our solar system from the Sun to the hypothetical Ort Cloud looked quite fixed at that point. In 2010, astronomer Mike Brown wrote a book titled How I killed Pluto and Why It Had It Coming. He had been at the forefront of Pluto’s nomenclatureral demise. Then in January of 2016, he and Konstantin Batygin (1986- ), would ironically propose the existence of a new planet, based on orbital perturbations, the same type of evidence that began the search for Pluto by Tombaugh.
The new non-Pluto Planet 9 begins its theoretical existence with a large mass of 60 000 Yottagrams, and an orbital distance that varies from 30 000 Gigameters to 180 000 Gigameters. It has a semi-major axis of about 105 000 Gigameters. Gigameter is the natural metric unit for describing the distances of planets in a solar system. Planet 9 is estimated to take about 10 000 to 20 000 years for a single orbit around the sun. Uranus, at 87 000 Yottagrams, is slightly more massive than the hypothetical Planet 9.
In June of 2017, Kat Volk, and Renu Malhotra, both from the University of Arizona, announced that computations they undertook indicate that a 10th planet exists. They estimate it is about 9000 Gigameters from the Sun and possesses a mass about that of Mars. Again, unexpected gravitational perturbations led researchers to suspect the existence of another planet, other than Planet 9.
In order to compare the two newly hypothesized planets, with our existing list of Planets, Kuiper Belt objects, and human created spacecraft; I have updated a table given in my essay Long Distance Voyager (about metric distances and the universe) which is presented below:
The first change I noticed is that if Planet 9 exists, Voyager 1 and Voyager 2 would no longer be “outside our solar system.” So are the Voyager Spacecraft still in interstellar space, or do we redefine them as inside our solar system? Categorization can be a difficult objective for astronomy, but where the Voyager spacecraft are, will probably not stir up the controversy that Pluto did when Eris was discovered. Eris is appropriately named for the Greek goddess of Strife and discord. The other categorization problem is that Planet 10 is well inside the orbit of Planet 9, so one would think they should swap numbers so Planet 10 is the furthest out and Planet 9 the next planet toward the Sun. Planet 10 also finds itself outside of the Kuiper Belt, and is probably a Trans-Neptunian planet, although how meaningful this designation would be remains to be seen. Planet 10 is between Pluto and Eris, and Planet 9 is the farthest hypothetical planet out by about an order of magnitude compared to Planet 10.
In many cases, astronomical masses outstrip the metric system, and one must resort to scientific notation, but in the case of our solar system, it might be useful to express the values using a large metric prefix. We will use Yottagrams, as that is the last magnifying metric prefix. Below is a table of Planetary Mass for selected objects in our solar system.
It is clear that Jupiter dominates the mass total of our solar system. One can estimate immediately that Jupiter is somewhere on the order of three times the mass of
the next most massive planet Saturn. Mercury, the smallest planet, is well over an order of magnitude more massive than Pluto or Eris. Pluto and Eris are an order of magnitude larger than Ceres the largest asteroid in the Asteroid Belt. It is clear that Jupiter, Saturn, Uranus, and Neptune form a Gas Giant mass class that is separate, and dominates all the other planets. The new Planet 9, should it exist, would be the runt member of this fraternity–unless it is not a Gas Giant, we then might need to implement a new designation from boxing and call them the Heavymass planets. The new Planet 10 would currently be grouped with the current Rocky planets, but from a distance perspective it would be the only member of this designation outside of the classical distance grouping of the inner and outer planets that are bounded on either side by the Asteroid Belt. Perhaps the less massive rocky planets could be called the Lightmass rocky planets, unless Planet 10 is gaseous? Whatever the Astronomical Union decides, the metric system is there for them, whether they use it, or not.
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The Metric Maven has published a book titled The Dimensions of The Cosmos. It examines the basic quantities of the world from yocto to Yotta with a mixture of scientific anecdotes and may be purchased here.